Project Summary/Abstract Alzheimer's Disease (AD) is the most common neurodegenerative disease that causes progressive decline in cognitive function. There is no effective intervention of AD, highlighting that development of therapeutics will require novel targets based on the identification of molecular pathways underlying AD pathophysiology. Many studies suggest that oligomers of 42 amino acid long amyloid- beta (A?42) drive the neural dysfunction leading up to or associated with AD. Early stages of AD pathogenesis include the loss of spine density and depressed glutamateric transmission in excitatory cortical and hippocampal neurons. Dysfunctional mitochondrial integrity in AD has also been postulated. However, it is unclear how the mitochondrial toxicity function in the pathogenesis of the disease. More importantly, molecular pathway that mechanistically connects these cellular changes is unknown. AMP-activated protein kinase (AMPK) is a key metabolic regulator activated by various metabolic stresses. One of its main functions is to maintain mitochondrial integrity in part by promoting mitochondrial fission via activation of mitochondrial fission factor (MFF), a mitochondrial outer membrane protein that recruits Drp1 fission protein, and mitophagy via activation of Unc-51 Like Autophagy Activating Kinase (ULK), proteins involved in the initial stages of mitophagy. Interestingly, hyperactivation of AMPK in a Calcium/ calmodulin activated kinase kinase II (CAMKK2) dependent manner has been observed in various AD models and patients, resulting in synaptotoxicity. Because AMPK also regulates many aspects of mitochondrial quality control, we hypothesized that AMPK is a novel master regulator in oligomeric A?42 induced synaptotoxicity and mitochondrial dysfunction via its downstream effectors, MFF and ULK. To test this hypothesis, we will use primary neuronal culture treated with oligomeric A? and J20 transgenic AD mouse model to look at spine density, mitochondrial morphology, and mitochondrial function after genetic manipulation of AMPK, MFF, and ULK proteins. Aim 1 will examine if hyperactivation of AMPK disrupts mitochondrial morphology and function that ultimately drives spine loss. Aim 2 will test if MFF functions in increased mitochondrial fission in an AMPK dependent manner. Lastly, Aim 3 will assess if ULK functions in disrupted mitophagy in an AMPK dependent manner. These studies will identify a novel molecular pathway involved in various early pathogenesis of AD and serve as a potential therapeutic target for AD.